Our project focuses on the biology, cell biology, molecular biology and biochemistry of activated lymphocytes, cells that are used for immunotherapy, especially for cancer treatment, and involved in the cellular immune response to xenogeneic tissues. In addition, we have initiated studies examining conditions of expression of porcine endogenous retrovirus under conditions that would be expected to be encountered in clinical xenotransplantation, with particular emphasis on cells of the immune system and factors that regulate them. Recently we have been examining how modulation of the redox environment affects the susceptibility of porcine endothelial cells to lysis by IL-2-activated human NK cells. TNF-alpha treatment upregulates the susceptibililty of these cells, while treatment of TNF-activated cells with oxidative stress together with nitric oxide reduces the cytotoxicity back to baseline levels. The mechanims of this reduction appears to involve the transcription factor, nuclear factor kappa B. We have expanded our studies of xenogeneic immune responses in the human anti-pig response in vitro. Our data show that NK cells are the primary mediators of the human vs. pig cytolytic cellular response, and that this response is up- regulated by several human cytokines, including IL-2, IL-12, IL-15, all of which would be expected to be produced in a xenograft recipient. In contrast, IL-18 and IL-8 have no effect. We are continuing to study how the NK-mediated xenogeneic response is modulated by redox conditions and beginning to investigate how the Gal(1-3)alpha Gal epitope participates in NK-mediated cytotoxicity against porcine target cells. Finally, we have data to suggest that certain cytokines may activate further porcine endogenous retrovirus expression in porcine bone marrow cells. However, this virus may not be infectious.